1. Field of the Invention
This invention relates to heat sealing techniques for effecting high volume sealing of scrim material and more particularly, in a preferred embodiment, to apparatus and methods for applying a thermoplastic tape to a bottom margin of a length of scrim reinforced tube stock material so that the tape is fused equally about a bottom edge of the tube stock.
2. Description of the Prior Art
In prior art tape delivery systems, it is well known to use tape forming techniques to prepare the shape of strips of thermoplastic tape for application to a bottom margin region of a length of tube stock or a blank of material during the fabrication of an open-mouth container bag. Various forming devices arrangements and mechanical motion strategies and combinations thereof, have been employed to develop efficient automatic, production line tape seal delivery systems to effect proper tape seals.
Most prior art tape delivery systems have been employed to weld thermoplastic films. Such a delivery system is described in U.S. Pat. No. 2,469,972 issued May 10, 1949 to Lowry et al. There a system is described which is capable of providing effective welds of thermoplastic tape along a bottom edge of thermoplastic tube stock, but, however, the structural arrangement of the component parts of the system and the tolerances thereof are not suited for application of thermoplastic tape to very thin and flexible thermoplastic material. Another method for automatic fabrication of bags is described in U.S. Pat. No. 4,106,261 issued Aug. 15, 1978 to Greenawalt. There, scrim reinforced web is converted into a tube and then the tube is fabricated into a plastic bag structure. The bottom and top ends of the bag structures are heat sealed after filling the container with a product. The fabrication of bags as disclosed in this patent appear to require tight control over the products that are placed in each bag; also an overlap seal of the marginal ends as described therein would not provide the strength and dimensional stability in both the warp and fill direction of the material to provide an effective bottom seal for an open-mouth bag.
It should be recognized that in fabricating open-mouth scrim reinforced bags of the type wherein the bottom margin of the scrim reinforced tube stock is sealed, the use of overlap sealing techniques would be impractical. Material structure of the plies of plastic would not permit sufficient adhesion to support the product load weights illustratively of 30-40 pounds.